The present invention relates to a clamp. More particularly this invention concerns a clamp usable as a vise for holding a workpiece.
A clamp is known having a fixed member or jaw relative to which a movable member or jaw is displaceable. A threaded spindle is typically provided for displacing this movable member along a guide relative to the fixed member to clamp a workpiece between these members. Such a system allows a relatively great clamping force to be made effective on the workpiece. This clamping force is applied at a mechanical advantage which is inversely proportional to the pitch of the screw thread. Thus when a screw thread of very flat pitch is used a relatively great mechanical advantage can be gained. On the other hand, however, the speed with which the two elements can be moved together is directly proportional to the steepness of the pitch so that with a relatively steeper pitch the two elements can be moved together and apart very rapidly. Thus it is necessary to trade off the desirability of a good mechanical advantage against the similarly desirable feature of quick opening and closing.
It has been suggested to provide a half nut on the movable member engageable with the spindle. Thus the half nut can be lifted off the spindle to allow the movable member to slide along this spindle and is thereafter engaged over the spindle for clamping action. Such an arrangement requires two hands to operate and frequently slips apart when considerable force is applied.